Stabilizers for chlorine-containing resins and process for producing the same

ABSTRACT

A stabilizer for chlorine-containing resins, comprising calcium hydroxide coated with a calcium salt of an organic acid, and a process for producing the same wherein calcium hydroxide and an organic acid are reacted at a molar ratio of 1 mole of calcium hydroxide: not more than 2 moles of organic acid in the presence of a medium and a surface active agent, while heating and stirring, to convert the outer surface of the calcium hydroxide to a calcium salt of the organic acid.

This is a continuation of application Ser. No. 632,036 filed Nov. 14,1975 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a stabilizer for chlorine-containingresins which is non-toxic, which serves to prevent secondary aggregationof the resins while they are being shipped, and particularly whichimproves the workability of the resins, and further to a process forproducing such stabilizers.

2. Description of the Prior Art

Examples of chlorine-containing resins used in this invention include,for example, polyvinyl chloride, most commonly commercially availablewith a chlorine content of around 56.6 wt%; polyvinylidene chloride,most commonly commercially available with a chlorine content of around73.2 wt%; a' vinyl chloride-vinylidene chloride copolymer; a vinylchloride-vinyl acetate copolymer, most generally commercially availablewith a vinyl acetate content of 0.4 to 40 wt%, more often 0.5 to 20 wt%;a vinyl chloride-ethylene copolymer, most generally commerciallyavailable with an ethylene content of 1 to 15 mole % and a meanmolecular weight of 700 to 1500; chlorinated vinyl chloride, mostgenerally commercially available with a chlorine content of 60 to 70wt%, more often 63 to 68 wt%; and chlorinated polyethylene, mostgenerally commercially available with a chlorine content of 25 to 45wt%. These materials undergo thermal decomposition during molding, andrequire a stabilizer to prevent such thermal decomposition. As laterwill be explained in detail, the present invention provides such astabilizer.

Heretofore, inorganic acid salts, organic acid metal salts, and organictin compounds have generally been used as such stabilizers.

Many of these stabilizers are toxic, e.g., those which contain lead, andaccordingly their use is limited. Recently, non-toxic calcium hydroxidewhich has thermal stability and is very inexpensive has come intopopular use.

However, particulate calcium hydroxide does not have a smooth surface,so that when the particulate calcium hydroxide or a chlorine-containingresin powder containing such particulate calcium hydroxide is shipped,or particularly when it is automatically fed, the calcium hydroxideaggregates (this phenomenon will hereafter be referred to as secondaryaggregation). This phenomenon eventually degrades the dispersibility ofthe calcium hydroxide in the chlorine-containing resin powder, ordegrades the quality of molded products made of such a mixture of ahigher proportion of the products must be rejected as unacceptable,because the calcium hydroxide migrates to the surface of the moldedproducts or adheres to metal molds.

SUMMARY OF THE INVENTION

Various investigations were conducted by the inventors to overcome thesedrawbacks, and they found that calcium hydroxide coated with a calciumsalt of an organic acid can be used as a non-toxic stabilizer forchlorine-containing resins which prevents secondary aggregation whilethey are being shipped, improves the workability of the resins uponmolding to a substantial extent, and imparts long-term thermal stabilityto the resins.

The primary object of the present invention is to provide a stabilizerfor chlorine-containing resins which comprises calcium hydroxide coatedwith a calcium salt of organic acid.

Another object of the invention is to provide a process for producingsuch a stabilizer, which comprises reacting calcium hydroxide with anorganic acid at a molar ratio of 1: not more than 2, in the presence ofa medium and a surface active agent, while heating and stirring.

DETAILED DESCRIPTION OF THE INVENTION

The term "medium" as is used herein means water or an organicsolvent(s). If desired, the water may contain a suspension stabilizer(such as a suspender, dispersant or surface active agent). Examples of"aqueous mediums" include water, an ammonia solution, an aqueous PVAsolution, etc. Examples of an organic solvent "medium" includeshydrocarbon solvents such as petroleum ether, cyclohexane, benzene,etc.; alcohol solvents such as methanol, ethanol, propanol, etc.;halogenated hydrocarbon solvents such as trichloroethane,perchloroethane, etc.; ether solvents such as amylphenyl ether, etc.;and ketone solvents such as acetone, methyl ethyl ketone, etc.; andcompatible mixtures thereof.

It is believed that calcium hydroxide disperses into an aqueous solutioncontaining a surface active agent in a suspended state rather thandissolving in the aqueous solution

Examples of suitable surface active agents used in this inventioninclude nonionic surface active agents such as polyoxyethylenealkylphenyl ethers, polyoxyethylene alkyl ethers, polyoxyethylene alkylesters, sorbitan alkyl esters, polyoxyethylene sorbitan alkyl esters,etc.; anionic surface active agents such as fatty acid salts, sulfuricacid esters of higher alcohols, sulfuric acid esters of aliphatic aminesor amides, etc.; cationic surface active agents such as aliphaticamines, quaternary ammonium salts, etc.; and mixtures thereof. Thesurface active agent provides a sufficient effect even in an amount ofless than 0.1% based on the total system weight. Surface active agentshaving an HLB (hydrophilic-lypophilic balance) of 4 to 17 are generallyused.

As organic acids useful in the present invention, there can beexemplified monocarboxylic acids (caprylic acid, capric acid, lauricacid, myristic acid, palmitic acid, stearic acid, behenic acid, acrylicacid, methacrylic acid, ricinolic acid, etc.), dicarboxylic acidmonoesters (monoesters of oxalic acid, malonic acid, succinic acid,glutaric acid, adipic acid, pimelic acid, suberinic acid, azelaic acid,sebacic acid, etc.), unsaturated dicarboxylic acid monoesters(monoesters of maleic acid, fumaric acid, citraconic acid, mesaconicacid, itaconic acid, aconitic acid, etc.), aromatic monocarboxylic acids(benzoic acid, salicylic acid, etc.), aromatic dicarboxylic acidmonoesters (monoesters of phthalic acid, terephthalic acid, etc.),thiocarboxylic acids (thioglyconic acid, mercaptolactic acid,mercaptopropionic acid, etc.), beef tallow hardened fatty acids, fishoil hardened fatty acids, and oxy fatty acids.

The preferred organic acids used in this invention include saturated andunsaturated fatty acids having 10 to 22 carbon atoms, such as capricacid, lauric acid, palmitic acid, stearic acid, arachic acid, oleicacid, ricinolic acid, etc.; dicarboxylic acid monoalkyl esters having 10to 22 carbon atoms, in which the alkyl moiety thereof has 1 to 4 carbonatoms, such as esters of oxalic acid, succinic acid, adipic acid,azelaic acid, etc.; unsaturated dicarboxylic acid monoalkyl estershaving 10 to 22 carbon atoms, in which the alkyl moiety thereof has 1 to4 carbon atoms, such as esters of maleic acid, fumaric acid, itaconicacid, etc.; monoaromatic monocarboxylic acids such as benzoic acid,salicylic acid, etc.; aromatic dicarboxylic acid monoalkyl esters having10 to 22 carbon atoms, in which the alkyl moiety thereof has 1 to 4carbon atoms, such as esters of phthalic acid, terephthalic acid, etc;thiocarboxylic acids such as thioglyconic acid, mercaptolactic acid; andbeef tallow hardened fatty acids, fish oil hardened fatty acids and oxyfatty acids, in which the fatty acid has 8 to 32 carbon atoms andmixtures thereof. The most preferred organic acids are stearic acid andpalmitic acid. The minimum amount of acid used is generally abut 2% byweight based on the Ca(OH)₂, and a preferred range for the acid in thestabilizer is from about 2 to about 10% by weight, based on the weightof the calcium hydroxide.

As a rule, the reaction between calcium hydroxide and the organic acid,e.g., stearic acid, proceeds as follows:

    Ca(OH).sub.2 +2C.sub.17 H.sub.33 COOH→(C.sub.17 H.sub.33 COO).sub.2 Ca+2H.sub.2 O

the theoretical stoichiometric molar ratio of calcium hydroxide tostearic acid required for the reaction is 1:2, but when an organic acidat a molar ratio of not more than 2 is reacted with calcium hydroxide inthe presence of a medium and a surface active agent, while heating andstirring, the outer surface or "shell" of the calcium hydroxide reactswith the fatty acid to form the corresponding calcium salt with thefatty acid, while the excess calcium hydroxide which does notparticipate in the reaction remains as a core, whereby the outer surfaceof the calcium hydroxide is coated with a calcium salt of the organicacid.

The reaction temperature is about 90° to 100° C. The reaction time isusually about 1 hour after the reaction system reaches the above-definedtemperature.

In theory, the higher the conversion of the acid into the calcium saltof the organic acid, the higher the efficiency. In practice on acommercial scale, the conversion of acid into the calcium salt of theorganic acid seems to be at most about 50% by weight of the acid.

If the thus obtained stabilizer comprising calcium hydroxide coated witha calcium salt of an organic acid is free from secondary aggregation ina hopper conduit during shipping, flows smoothly to enable easyautomatic feeding and if it is mixed with a chlorine-containing resinpowder, white calcium hydroxide is prevented from migrating to thesurface of molded products made be extruding such a mixture or formadhering to metal molds. The stabilizer of this invention can be mixcedwith stabilizers, fillers, pigments, lubricants, etc., if desired.

The stabilizer is generally added in an amount of 0.5 to 10% by weightof the system it is blended with.

The following Examples illustrate the invention. All processings wereconducted at room temperature, atmospheric pressure and all percentages,parts and ratios were by weight, unless otherwise indicated in thefollowing Examples.

EXAMPLE 1

1 liter of water and 400 g of calcium hydroxide were placed in a vesseland stirred at 90° C. to form emulsion (A). 50 cc of water, 40 cc of a25% ammonia solution, 0.4 g of Monogen ET-170 (a product of DaiichiKogyo Seiyaku Co., Ltd.; a polyoxyethylene alkylphenyl ether surfaceactive agent) and 8 g of stearic acid were placed in another vessel andstirred at 90° C. to form emulsion (B). Emulsion (B) was gradually addedto emulsion (A) over a period of 30 minutes, while stirring at roomtemperature The mixed emulsion was kept at a predetermined temperatureranging from 70° to 100° C., preferably 95° to 100° C., for one hour andthereafter allowed to stand sufficiently to cool, whereupon it wasdehydrated by centrifugal separation. (Standing is a simple way tocomplete the reaction of stearic acid added and calcium hydroxide.)After drying in a conventional manner there was obtained a stabilizer inthe form of powdery particles.

2 Grams of this stabilizer was placed in a beaker, and 50 cc of methylalcohol as a neutral alcohol added thereto. After allowing the mixtureto stand at room temperature for 30 minutes with occasional stirring tocomplete the elution of unreacted stearic acid, the contents of thebeaker were filtered in vacuo using a Nutsche funnel and a pressurebottle. The residue was washed three times with methyl alcohol, and allwashings were titrated with 0.05 N NaOH to determine the amount of freestearic acid according to the following formula: ##EQU1## f: titer of a0.05 N sodium hydroxide standard solution (The molecular weight ofstearic acid is 275.)

Table 1 shows the amount (%) of free acid based on the starting stearicacid, in the treatments at 70°, 80°, 90°, 95° and 100° C., respectively.

                  Table 1                                                         ______________________________________                                                          Example 1                                                                     (1) (2)   (3)    (4)  (5)                                   ______________________________________                                        Reaction temperature (° C.)                                                                70    80    90   95   100                                 Amount (%) of free stearic acid                                                                   75    19    6.5  2.5   0                                  ______________________________________                                    

As will be seen from Table 1, the amount of free stearic acid withrespect to the starting stearic acid, in the product which can beobtained at a reaction temperature of 70° C.-Example 1 (1)-is 75%, andit assumed that the remaining 25% stearic acid reacted with calciumhydroxide to form calcium stearate. In the case of Examples 1(4) and1(5), where the reaction temperature was 95° C. and 100° C.,respectively, 97.5% and 100%, respectively, of the stearic acid wasassumed to have been reacted with calcium hydroxide to be converted intothe calcium stearate. It can thus be concluded that the conversion ofstearic acid into calcium stearate takes place more easily at 95°-100°C.

Further, the amount of the stearic acid initially added was much lessthan 2 mols per mole of calcium hydroxide. The use of such a smallamount of stearic acid makes it possible to effect a uniform reactionwith the calcium hydroxide in the medium, whereby only the outer surfaceof the calcium hydroxide stabilizer is converted into calcium stearate,with the excess calcium hydroxide not participating in the reactionremaining as a core, thus forming a stabilizer of calcium hydroxidecoated with calcium stearate.

In all examples the particle size distribution of the calcium hydroxideused was as follows, in which the defined values refer to the amountswhich remain on the sieve size recited.

    ______________________________________                                         40 mesh         0.2%                                                          60 mesh         8.4                                                          100 mesh         26.15                                                        150 mesh         26.4                                                         200 mesh         29.35                                                        others           29.25                                                        ______________________________________                                    

EXAMPLE 2

100 Parts by weight of polyvinyl chloride was mixed with 3 parts byweight of calcium hydroxide treated according to Example 1(5), exceptfor varying the amount of stearic acid as indicated in Table 2. Theresulting mixtures were subjected to the Congo Red test at 190° C. basedon JIS K 6732. The thermal stability test results are shown in Table 2as Examples 2(1)-(3).

Comparative Example 1 relates to the case where 3 parts by weight ofcalcium hydroxide alone was added, and Comparative Examples 2 to 4relate to the cases where 3 parts by weight of a mere mixture of calciumhydroxide and calcium stearate in an amount proportional to that used ineach of Examples 2(1) to (3) was added.

                  Table 2                                                         ______________________________________                                                  Example 2  Comparative Examples                                               (1)  (2)    (3)    1    2    3    4                                 ______________________________________                                        Polyvinyl chloride                                                                        100    100    100  100  100  100  100                             Calcium hydroxide                                                                         --     --     --   3    2.94 2.91 2.85                            Calcium stearate                                                                          --     --     --   --   0.06 0.09 0.15                            Coated calcium                                                                            3      3      3    --   --   --   --                              hydroxide (amount                                                             of stearic acid                                                                           (2%)   (3%)   (5%)                                                before reaction)                                                              Thermal resistance                                                            time (min. second)                                                                        15.10  16.30  21.50                                                                              13.00                                                                              13.00                                                                              13.00                                                                              14.00                           ______________________________________                                    

The thermal resistance time in Comparative Example 1, where only calciumhydroxide was added, was 13 minutes, while that in each of Examples2(1)-(3) where the calcium hydroxide coated with calcium stearate wasadded (the amount of the stearic acid used for the reaction based on thecalcium hydroxide was respectively 2%, 3%, and 5%) was extended (15.10minutes, 16.30 minutes and 21.50 minutes, respectively).

The thermal resistance times in Comparative Examples 2 to 4 whereincalcium hydroxide and calcium stearate were used in combination in theamounts as indicated in Table 2, respectively correspond to those ofExample 2(1) to (3), i.e., 13.00 minutes vs. 15.10 minutes, 13.00minutes vs. 16.30 minutes and 14.00 minutes vs. 21.50 minutes. Theseresults establish that the use of the "coated" calcium hydroxides of theinvention provides longer thermal stability than the use of a meremixture of calcium hydroxide and calcium stearate as in the ComparativeExamples.

EXAMPLE 3

A test on flowability was conducted as follows: 50 g each of the coatedcalcium hydroxides prepared by the method of Example 1(5) and untreatedcalcium hydroxide were poured into conventional funnels 170 mm tall, theconical top of the funnel being 90 mm tall and 90 mm in diameter acrossthe top, and the tubular section of the funnel extending from theconical top being 80 mm long and having various diameters as shown inTalbe 3. The conical walls of the funnel made an angle of 70° withrespect to horizontal. Upon removing the stopper of each funnel, theslump was measured. The results are shown in Table 3.

                  Table 3                                                         ______________________________________                                        Diameter of funnel (mm)                                                                         5     10    15  20  30  40  50                              Untreated calcium hydroxide                                                                     X     X     X   X   Δ                                                                           O   O                               Coated calcium hydroxide                                                                        X     Δ                                                                             O   O   O   O   O                               ______________________________________                                         O : slump of substantially all powder                                         Δ : partial slump of powder                                             X : no slump of powder                                                   

As is seen from Table 3, the coated calcium hydroxide of the inventionhas good flowability, totally slumping in funnels of a 15 mm or a largerdiameter, while the untreated calcium hydroxide did not slump in funnelsof up to 30 mm in diameter.

With specimens similar to the above, the repose angle (angle withrespect to horizontal of the slope naturally formed when a powderysubstance is heaped) was measured. In the case of the untreated calciumhydroxide, the angle was 53°08', while in the case of the coated calciumhydroxide prepared by the method of Example 1(5) of the presentinvention, it was 48°11', proving reduced secondary aggregation andimproved flowability. Untreated calcium hydroxide has considerableinter-particle friction and also strong inter-particle affinity, whichcause formation of secondary aggregation of calcium hydroxide alone, inthe course of transportation. On the other hand, the smooth film formedwith calcium stearate over the outer surface of calcium hydroxide inaccordance with the present invention serves to reduce the secondaryaggregation of the particles, and thus provides remarkably improvedflowability.

EXAMPLE 4

A powdery mixture of 100 parts by weight of polyvinyl chloride, 3 partsby weight of the coated calcium hydroxide of Example 1, 1.5 parts byweight of calcium stearate, 0.7 part by weight of montanic acid esterwax, 0.5 part by weight of low molecular polyethylene (averagepolymerization degree: 2000) and 0.3 part by weight of a pigment wassubjected to an extrusion test with a 90 mm twin screw extruder providedwith a 40 mesh screen (between the extruder and the die) and a die for60 mm diameter plastic pipe.

An identical mixture except for substituting untreated calcium hydroxidefor the coated calcium hydroxide was used as a control.

In the case of the control, secondary aggregation of white calciumhydroxide was observed on the surface of the pipe at a rate of oneoccurrence for every 1 m of pipe length. In the case of the presentinvention, no such aggregation was observed.

The mixtures were also subjected to independent continuous extrusion toobserve the condition of the metal mold and the screen. In the case ofthe untreated calcium hydroxide, on the third day the screen was pluggedwith secondary aggregates and, after 7 working days, the mold wasremoved to discover a brownish solid substance adhered in a 0.5-1 mmthickness over the entire chromium-plated surface of the metal mold. Inthe case of the present invention, while on the 6th day the screen wasfound to be plugged with sand, dusts, impurities, cabonaceous materialsand the like, it was not plugged with a secondary aggregate, and after14 working days, the metal mold was removed with no adhesion on thechromium-plated surface thereof.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A process for producing a thermal stabilizer forchlorine-containing resins which comprises calcium hydroxide coated witha calcium salt of an organic acid selected from the group consisting ofsaturated fatty acids having 10-22 carbon atoms and mixtures thereof,where calcium hydroxide and said organic acid are reacted at a molarratio of 1 mole of calcium hydroxide: not more than 2 moles of saidorganic acid, in the presence of an aqueous medium and a surface activeagent selected from the group consisting of polyoxyethylene alkylphenylethers, polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters,fatty acid salts, sulfuric acid esters of higher alcohols, sulfuric acidesters of aliphatic amines or amides, quaternary ammonium salts andmixtures thereof, while heating and stirring at about 90° to 100° C., toconvert the outer surface of the calcium hydroxide into a calcium saltof said organic acid.
 2. The process of claim 1, wherein said organicacid is selected from the group consisting of stearic acid and palmiticacid.
 3. The process of claim 1, wherein said calcium salt comprisesfrom about 2 to about 10 wt% of said organic acid, based on the weightof said calcium hydroxide.